Summary of Work: Uranium miners are at increased risk for lung cancer mortality. Risks for other cancers have not been consistently shown. Risk has been most clearly demonstrated for miners exposed to very high levels of radon under extremely poor working conditions. The relevance of these results to more recent miners or to individuals exposed to radon in the home is not known. We studied uranium miners from the Czech Republic, taking advantage of previously classified records for miners exposed to modest levels of radiation. We collected data on smoking and dust exposure, both important potential confounding factors. We are also the first study to investigate cancer incidence using linkage with a population-based cancer registry. At total of 18,985 miners worked at least one year underground between 1949 and 1976. Vital status was determined for all but 511. Using a variety of sources, we identified 1944 incident cancers through 1992 for the 16,434 miners known to be alive and still resident in the CR on 1/1/77. Compared with the entire CR, miners had more than twice the expected incidence rate of lung cancer. Risk increased with increasing years of underground mining and with increasing cumulative radiation exposure. Lung cancer risk was increased for miners with cumulative exposures that were consistent with doses possible to accumulate after lifetime residence in a high radon US home. Risk did not appear to be due to confounding by smoking or dust exposure, but these exposures will be explored in greater detail in a case-cohort analysis. The incidence of cancers other than lung cancer was only slightly increased among miners. However, there was significantly increased risk for some specific cancers including leukemia for which there was a dose-response trend. Increased incidence rates were seen for cancer of the larynx, stomach, liver, and colon and rectum, but no dose-response trends were observed. Risk for some of these other cancers may be explained by other exposures in the mines or by other characteristics of the miners. Additional years of follow-up are planned to better assess some of these potential risks.